A multitude of optical fiber splicing devices are available, by which the ends of optical fibers are connected to each other by “thermal splicing”. The processes used for this are suitable for singlemode as well as multimode optical fibers as well as for fiber ribbons. The substance-determined connection of the ends of the fibers takes place by heating and fusion by means of corona discharge, which occurs between two electrodes. In the formation of an optical fiber network a significant number of connections have to be made, so that adequate optical fiber splicing devices were developed. By means of these devices the processing steps necessary for connections such as the approaching of the ends of the optical fibers to be connected, their positioning and alignment and finally the actual splicing were coordinated and brought together into specially designed optical fiber splicing devices. Additionally, suitable lighting and monitoring instruments are used in these devices, through which the progress of the process can be monitored.
Such optical fiber splicing devices can be found in the following literature:    Telekom report 19 (1956), issue 1; pages 39–42    Telekom report 18 (1995), issue 3; pages 136–139    Telekom report 13 (1990), issue 2; pages 62–65    Telekom report 9 (1986), issue 3; pages 197–201    ICCS and Future-Link; catalogue 1998; Siemens-Communications-Cable Networks; pages 107–116    DE4235924-C2
The attenuation of a splice connection performed with such an optical fiber splicing device depends on the exact alignment of the light-guiding fiber cores, the quality of the fiber end faces and on the relevant splicing parameters selected. Thus in thermal connection technology, optical waveguides or optical fibers, respectively, (referred to as “fiber” in the following) are spliced together by heating two exactly aligned fiber ends to melting temperature. In this viscous state, the two ends of the fibers are pushed into each other, so that it leads to the mutual fusion of the ends of the fibers and they are thereby thermally connected. The fiber heating is performed by a corona discharge, which builds up after igniting between two electrodes.
The desired objective of the thermal connection technology is the formation of splice connection with the least possible attenuation values. With a modern splicing device under favorable conditions, median attenuation values under 0.02 dB are possible. In order to realize these low attenuations, precisely set parameters, so-called splice parameters, are necessary in addition to exactly prepared fiber ends. Important splice parameters include splicing voltage, splicing time, and the thrust with which the fiber ends are pushed towards each other. The perfectly set splicing voltage causes an optimal viscosity of the fiber ends during heating by the electrical corona discharge, so that in concert with the set splicing time and the set thrust, splice connections with small attenuation result. Optimal splicing results can only be obtained with optimal outside conditions (no air movement, normal humidity and room temperature, steady atmospheric pressure and other parameters) and with the perfect condition of the splicing device. It is also especially important that there are no contaminations of the electrodes and the fiber guides.
During prolonged use of the optical fiber splicing device, a certain contamination due to material diffusion during the splicing process and burning off of the electrodes occurs. Thus, a higher impedance results at the contamination point, so that the corona discharge avoids this point, that is, the corona discharge does not build up equally around the electrode tip. During the next splicing process, an evaporation of the old contamination occurs in addition to new material diffusion, which then settles again on the electrodes. It can be seen from this, that in the course of time very variable conditions result on the electrodes, which can uncontrollably alter the condition of the corona discharge. The corona discharge is then no longer stable between the two electrodes and a flickering of the corona discharge results. A further cause for an unstable corona discharge can also be found in the surface condition of the electrode tips. A rough electrode, not formed rotation-symmetrical, can also lead to a flickering corona discharge due to thermal air movement created during the splicing process. This leads to irregular, not reproducible fiber heating. The result of this, that the quality of the fiber connection in certain cases can vary greatly. With flickering of the corona discharge it can happen that the area of the greatest heating forms above or below the splice point, so that the originally expected heating at the ends of the fibers is not achieved, or is not achieved in a timely manner. Looking in the fiber longitudinal direction, an unstable corona discharge thus leads to a heating of a larger fiber area in comparison to heating with clean electrodes. These deviations cause an irregular fiber heating at the splice point even with unchanged splicing voltage, which results in an undefined material flow. This leads to a deterioration of the splice attenuation result. Besides the electrode contamination, flickering corona discharge can also be caused by air movement, where the previously mentioned problems can also occur. Additionally, due to burning off of the electrodes, changes in the electrical corona discharge can occur, since the distance between the electrodes increases.
With such thermal splicing devices, the electrodes and the environment of the corona discharge are completely open, so that the corona discharge is completely exposed to the environmental conditions. With these devices, the avoidance of an unstable corona discharge can only be achieved by constantly cleaning or replacing the electrodes. Another possibility for avoiding the instability would be an adjustment of the splicing voltage, so that the fiber temperature at the splice point corresponds to the ideal temperature. This is, however, very time-consuming and leads to only a conditional improvement of the splicing results since constantly changing temperature conditions at the splice point result due to the non-reproducible flickering of the corona discharge. Additionally, it is not possible to remove the effects of the asymmetrical fiber heating by such means.
The present invention has the objective to stabilize the corona discharge during thermal splicing of optical fibers in an optical fiber splicing device. This objective is achieved with an optical fiber splicing device of the initially explained type, by arranging a corona discharge guide in the area of the corona discharge surrounding the electrodes.
A decisive advantage over the state of the art technology lies in the fact that a corona discharge guide is added in the construction of the corona discharge area according to the invention, with which the electrodes and the corona discharge are largely protected against environmental influences. This corona discharge guide consists essentially of a surrounding tube or profile body, in whose inner space the corona discharge is constructed. Two small tubes are inserted between the two electrodes into the corona discharge length, so that the corona discharge is guided within the tubes to the immediate area at the ends of the optical fibers to be connected. The dimensions of the tubes have to be such that the same temperature conditions exist at the ends of the fibers with clean, non-flickering electrodes as without tubes, that is, the corona discharge has to be able to spread unimpeded in each case. As mentioned before, a flickering corona discharge results in temporary direction changes of the corona discharge, which leads to the described irregularities. Such a detour or deflection is avoided due to the measures according to the invention based on the spatial guiding of the electrical corona discharge in the area of the electrodes. This leads to the light arc position at the splice point remaining constant, even with a local detour near the electrodes. Additionally, the use of the corona discharge guide has the advantage that there is less burning off and that the increased electrode distance in the area of the splice point due to burning off in the area does not appear.
For the material of the light arc guide, a non-electricity-conducting, low thermal conducting material, which additionally has to be heat, ozone and UV resistant is necessary. Especially suitable is therefore ceramic or quartz glass material.
As corona discharge guide in the concept of the invention a continuous tube between the electrode can also be used, where corresponding openings for the insertion of the ends of the fibers and corresponding observation channels for monitoring the splicing process are provided in the area of the connection point of the optical fibers. This leads to an additional advantage, since the corona discharge is guided over a much greater area. Thus, a still better stabilization of the electrical corona discharge can be achieved.
A further construction sample for a corona discharge guide according to the invention results from the use of a continuous tube, which is divided in longitudinal direction in such a way that two complimentary longitudinal parts result. The tube should be divided into two equal parts in the longitudinal direction. It is advantageous for the lower part of the tube to be fastened tightly into the splicing device or the spark gap of the splicing device, respectively, and for the upper part to be attached in a hinged manner. It is advantageous to combine the upper part with the electrode hinge of the spark length so that only one hinge process is necessary. Corresponding openings for the insertion of the ends of the fibers and for monitoring also have to be provided here in the area of the connection point. The advantage of this construction lies in the fact that the corona discharge is also guided and protected over a larger area and that the ends of the fibers to be connected can be inserted much easier at the connection point. Additionally, the mechanical cleaning of the electrodes is much easier with the hinged tube.
An additional improvement of the corona discharge stability can be achieved when the necessary openings in the area of the connection point are closed off with an additional removable cover, where only the tiny observation channels and the insertion openings are open to the environment. It is also advisable that the cover is connected to the electrode hinge so that only one hinge process has to be performed.